Energy requirement for foliage formation is not constant along canopy light gradients in temperate deciduous trees

Abstract

Foliage construction cost (glucose requirement for formation of a unit foliar biomass, G, kg glu kg −" ), chemical composition and morphology were examined along a light gradient across the canopies in five deciduous species, which ranked according to increasing shade-tolerance as Populus tremula Fraxinus excelsior Tilia cordata l Corylus avellana Fagus sylvatica. Light conditions in the canopy were estimated by a hemispheric photographic technique, allowing ranking of sample locations according to long-term light input incident to the sampled leaves (relative irradiance). G and foliage carbon concentration increased with increasing relative irradiance in F. excelsior, T. cordata and C. avellana, but were independent of irradiance in F. sylvatica and P. tremula. However, if G of non-structural-carbohydrate-free dry mass was considered, it also increased with increasing relative irradiance in P. tremula. A positive correlation between the concentration of carbon-rich lignin and irradiance, probably a result of the acclimation to greater water stress at higher light, was the major reason for the lightdependence of G. Lignin concentrations were highest in more shade-tolerant species, resulting in greatest carbon concentrations in these species. Since carbon concentration and G are directly linked, the leaves of shade-tolerant species were also more expensive to construct. As the result of these effects, G increased faster with increasing leaf dry mass per area which was mainly determined by relative irradiance, in shade-tolerators. Given that shadetolerant species had lower leaf dry mass per area at common irradiance and that this saturated at lower relative irradiance than leaf dry mass per area in the intolerant species, it was concluded that enhanced energy requirements for foliage construction might constrain species morphological plasticity and the upper limit of leaf dry mass per area attainable at high light.

Does ontogeny modulate irradiance-elicited plasticity of leaf traits in saplings of rain-forest tree species? A test with Dicorynia guianensis and Tachigali melinonii (Fabaceae, Caesalpinioideae)

“…In T. melinonii leaf thickness and carbon content were independent of irradiance in ASD 1 while density increased; this contradicts partly the hypothesis that high leaf density may be partly associated with the presence of tissues with high lignin contents (Niinemets, 1999b;Niinemets and Kull, 1998).…”

A comparative analysis of foliar chemical composition and leaf construction costs of beech (Fagus sylvatica L.), sycamore maple (Acer pseudoplatanus L.) and ash (Fraxinus excelsior L.) saplings along a light gradient

“…LMA increases with increasing irradiance, a reaction which most plants -if not all -show in such a pronounced manner that LMA even has been proposed as a suitable species-specific estimator of long term light climate (Niinemets, 1997). The modification in leaf morphology is further accompanied by changes in foliar chemistry (Niinemets, 1999). A lower LMA in low light is coupled with lower nitrogen content per unit leaf area (N a , * Corresponding author: apetrit@gwdg.de g N m −2 ) and lower photosynthetic capacity per unit leaf area (Frak et al, 2001;Le Roux et al, 2001).…”

“…But reports on the response of CC to varying irradiance are not consistent. Whereas some authors found CC to be lower at high light (Sims and Pearcy, 1994), others show higher values at high light (Barthod and Epron, 2005;Niinemets, 1999;Poorter et al, 2006). All these morphological and physiological leaf acclimation to varying irradiance are thought to contribute to shade tolerance of tree species.…”

“…To what extent these attributes of shade tolerance influence leaf construction costs has rarely been studied. Niinemets and Kull (1998) and Niinemets (1999) published the assumption that leaves of shade-tolerant species should contain more carbon and hence be more expensive to construct than leaves of shade-intolerant species.…”

“…Niinemets and Kull (1998) found that lignin concentrations increased at the expense of cellulose and hemicellulose with increasing irradiance. Inasmuch as lignin contains more carbon than cell wall polysaccharides, and as carbon concentration and the energetic costs of foliage construction (CC, g glucose g −1 , Vertregt and Penning de Vries, 1987) are directly linked, Niinemets (1999) assumed that leaf construction requires more energy Article published by EDP Sciences with increasing irradiance. But reports on the response of CC to varying irradiance are not consistent.…”